1. Field of the Invention
The present invention is directed to apparatus and methods for treating tissue with ultraviolet light.
2. Description of the Related Art
Skin disorders, including atopic dermatitis, dyshidrosis, eczema, lichen planus, psoriasis, and vitiligo, are conditions that commonly affect large populations at some time in their lives. For example, about 2% to 3% of the population of northern Europe is estimated to be afflicted with psoriasis. Although the disease's prevalence in the United States is not as well understood, it appears that between 150,000 and 260,000 new cases are diagnosed each year. This suggests that at least several million people suffer from the disease in the United States.
Psoriasis can range in severity from relatively mild, with some drying and flaking of the affected skin, to severe cases with very severe outbreaks over large areas of the patient's body. Even very mild psoriasis is uncomfortable and unsightly. Severe cases can be physically and psychologically debilitating, presenting a very serious threat to the patient's overall health.
Although the underlying mechanisms of psoriasis are not yet perfectly understood, the disease involves abnormally rapid cell proliferation in the basal layer of the skin. This hyperproliferation can be reduced and the disease ameliorated with what is conventionally known as “phototherapy,” i.e., by exposing the affected skin surface to a source of light, in particular, ultraviolet light. Phototherapy can be performed simply by exposing the patient to natural sunlight, or in a more controlled way by applying light from an artificial source to the affected areas.
Commonly, a patient may be exposed over substantially his or her entire body, or at least a very large portion of it, to artificial light from an electric lamp or a similar source generating light having a significant ultraviolet component. While this mode of treatment has been effective, it is less than optimal. In recent times patients and physicians have become increasingly aware of the undesirability of unnecessary exposure to ultraviolet light. Ultraviolet light causes damage to the skin and premature aging; it is also associated with melanoma and skin cancer. Additionally, conventional phototherapy treatment is implemented over an extended time and requires the patient comply to a regimen involving frequent visits to the physician before experiencing even slight improvement in his or her condition. Following such regimen is inconvenient to the patient as well as costly; furthermore treatment often fails due to lack of compliance to this regimen. Thus, what is needed is a treatment for psoriasis and other skin or tissue disorders that reduces side effects such as the risk of melanoma and skin cancer and that effectuates a rehabilitation of disease tissue expeditiously.